Wenbo Dong

Sulfate Radical Photogeneration Using Fe-EDDS: Influence of Critical Parameters and Naturally Occurring Scavengers.

In this study, the activation of persulfate induced by Fe(III)-ethylenediamine-N,N′-disuccinic acid (EDDS) under dark and irradiation conditions and the reactivity of the generated sulfate radical (SO4•–) under a wide range of experimental conditions were investigated by means of experimental kinetic analyses and modeling. The Fe(III)-EDDS induced activation of persulfate was found to be efficient across a wide range of pH value (3–7), whereas the second order rate constant of SO4•– with 4-tert-butylphenol (4tBP) kSO4•–,4tBP = (4.21 ± 0.22) × 109 M–1 s–1 was found to be unchanged between pH 2.5 and 8.5. Experimental and theoretical investigations showed clearly that the 4tBP degradation was enhanced in the presence of chloride (10 mM), whereas an almost complete inhibition was observed in the presence of carbonates (10 mM). For the first time, second order rate constants evaluated by laser flash photolysis experiments revealed that SO4•– has a similar reactivity with EDDS (6.21 × 109 M–1 s–1) and 4tBP (4....

Photolysis of low concentration H2S under UV/VUV irradiation emitted from microwave discharge electrodeless lamps

The photolysis of simulating low concentration of hydrogen sulfide malodorous gas was studied under UV irradiation emitted by self-made microwave discharge electrodeless lamps (i.e. microwave UV electrodeless mercury lamp (185/253.7 nm) and iodine lamp (178.3/180.1/183/184.4/187.6/206.2 nm)). Experiments results showed that the removal efficiency (eta H2S) of hydrogen sulfide was decreased with increasing initial H2S concentration and increased slightly with gas residence time; H2S removal efficiency was decreased dramatically with enlarged pipe diameter. Under the experimental conditions with pipe diameter of 36 mm, gas flow rate of 0.42 standard l s(-1), eta H2S was 52% with initial H2S concentration of 19.5 mg m(-3) by microwave mercury lamp, the absolute removal amount (ARA) was 4.30 microg s(-1), and energy yield (EY) was 77.3 mg kW h(-1); eta H2S was 56% with initial H2S concentration of 18.9 mg m(-3) by microwave iodine lamp, the ARA was 4.48 microg s(-1), and the EY was 80.5mg kW h(-1). The main photolysis product was confirmed to be SO4(2-) with IC.

Activation of persulfate by Fe(III) species: Implications for 4-tert-butylphenol degradation

In this study, the activation of persulfate induced by Fe(III) species, including 5 kinds of iron oxhydroxides (IOs) and dissolved Fe3+ under dark condition were investigated. Ferrihydrite (FH) and akaganeite (AK) showed the highest activity in 4-tert-butylphenol (4tBP) removal. The 4tBP degradation rate constant decreased as the solution pH increased from pH 3.2 to 7.8 in FH/S2O82- system. However, the pH value had no significant effect on the 4tBP degradation in AK/S2O82- system. The degradation of 4tBP in Fe3+/S2O82- system was also performed to investigate the role of ferric species in persulfate activation. The pH dependency of 4tBP degradation rate was closely related to the speciation of FeIII, whereas the Fe(H2O)63+ was found to be the most active soluble iron complex form in the activation of S2O82-. 4tBP degradation was mainly due to the SO4- in IOs/S2O82- system, while SO4- and HO2 both had great contribution on 4tBP degradation in Fe3+/S2O82- system. Further investigations showed clearly that 4tBP degradation efficiency was decreased significantly due to the trapping of SO4- by chloride. This finding may have promising implications in developing a new technology for the treatment of contaminated waters and soils, especially where Fe3+ species are naturally occurring.

Removal of H2S from gas stream using combined plasma photolysis technique at atmospheric pressure.

In this paper, H(2)S in gas stream was successfully decomposed at atmospheric pressure by dielectric barrier discharge plasma and VUV-UV radiation from a combined plasma photolysis reactor (CDBD). In comparison with DBD, CDBD enhanced H(2)S removal efficiency significantly at the same applied voltage, inlet H(2)S concentration and gas residence time. H(2)S removal efficiency was determined as a function of Kr pressure, applied voltage, inlet H(2)S concentration, and gas residence time. H(2)S removal efficiency could reach as high as 93% at inlet H(2)S concentration of 27.1 mg m(-3), residence time of 0.4 s, and applied voltage of 7.5 kV. The main products were discerned as H(2)O and SO(4)(2-) based on FTIR and IC analysis.

Toward a Better Understanding of Fe(III)−EDDS Photochemistry: Theoretical Stability Calculation and Experimental Investigation of 4-tert-Butylphenol Degradation

The present work describes in detail the chemical structure of the complex Fe(III)–EDDS and the predominance of different species with respect to pH. These results were obtained with ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed, and HO(•) is the main species responsible for the degradation of the organic compound present in aqueous solution. The degradation of 4-tert-butylphenol (4-t-BP), used as a model pollutant, was investigated in different conditions. For the first time, the second-order rate constant of the reaction between HO(•) and 4-t-BP and the formation rate of HO(•) (R(HO(•))(f)) from the photochemical process were evaluated. Through the degradation of 4-t-BP, the effect of Fe(III)–EDDS concentration, oxygen, and pH was also investigated. The pH, which plays a role in the iron cycle and in the Fe(III)–EDDS speciation, was noticed as an important parameter for the efficiency of 4-t-BP degradation. Such a result could be explained by taking into account the complex speciation and presence of a predominant form (FeL–) up to pH 8. These results are very useful for the use and optimization of such iron complexes in water treatment processes.

Photodegradation of carbamazepine with BiOCl/Fe3O4 catalyst under simulated solar light irradiation

A magnetic BiOCl/Fe3O4 catalyst with simulated solar light response was successfully prepared through a precipitation process and characterized by X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, VSM, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy. The photocatalytic activity of BiOCl/Fe3O4 nanocomposites was further investigated through the photodegradation efficiency of carbamazepine (CBZ). In this study, 90.3% of CBZ was removed after 60min irradiation in the presence of the BiOCl/Fe3O4 catalyst. Three reactive species were identified; the contribution of h+, HO, and O2- to CBZ degradation was approximately 94.98%, 3.25%, and 1.06%, respectively. The pH value had a significant effect on the CBZ degradation, and the best performance was achieved at pH 2.68. The presence of common anions (NO3-, Cl-, CO32-, and SO42-) also affected the CBZ degradation. The inhibiting effect followed the order of CO32->SO42->Cl-. However, NO3- weakly favored the photodegradation of CBZ. Moreover, the BiOCl/Fe3O4 photocatalyst could be easily recollected from the solution by applying an external magnetic field. This type of magnetic photocatalyst, which is characterized by ease of separation, may have application potential in wastewater treatment. The disappearance of CBZ as well as the formation of its products were determined by liquid chromatography mass spectroscopy and the possible photocatalytic degradation pathways were proposed.

Preparation and formation mechanism of BiOCl0.75I0.25 nanospheres by precipitation method in alcohol-water mixed solvents.

BiOCl0.75I0.25 crystals with irregular three-dimensional (3D) flower-like and hierarchical nanosphere-like structures were successfully synthesized in different alcohol-water mixed solvents by precipitation method. The primary formation mechanism of BiOCl0.75I0.25 nanospheres was investigated by taking water, monohydric alcohols (ethanol and isopropanol), and polyhydric alcohols (ethylene glycol, diethylene glycol, and glycerol) as solvents in the synthesis process. The obtained BiOCl0.75I0.25 samples were characterized by powder X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and nitrogen adsorption. Results showed that the alcohol solvents with different physical and chemical properties used in the synthesis process performed significant functions in directing the morphology and surface pore structure of BiOCl0.75I0.25 crystals. Meanwhile, BiOCl0.75I0.25 synthesized in various solvents exhibited morphology-dependent adsorption and photocatalytic degradation abilities in removing p-hydroxyphenylacetic acid (p-HPA), which was used as a model pollutant, in aqueous solutions under simulated solar light (λ⩾290nm). In addition, the fabrication process of the crystal products was proposed through a series of time-dependent experiments.

Study on the reaction of carbon disulfide with hydroxyl radical in aqueous solution

The laser flash photolysis technique is employed to investigate the reaction mechanism of CS2 with ·OH in the nitrogen-saturated aqueous solution. By comparison of the transient absorption spectra obtained at different phases and pHs and through the addition of proper radical cation scavenger, CS2 is determined to react with · OH to form · CS2OH adduct, instead of the CS2+ radical cation. At pH 1–5, · CS2OH decomposes into COS and · HS, while at pH > 5, it further reacts with OH- to form CS2O-. The temperature dependent kinetics for the reaction CS2 + · OH → · CS2OH is also reported in this paper with an estimated activation energy of (26.9±1.0) kJ · mol−1.

Photodegradation of 4-tert-butylphenol in aqueous solution by UV-C, UV/H2O2 and UV/S2O82− system

ABSTRACT The photolytic degradation of 4-tert-butylphenol (4-t-BP) in aqueous solution was investigated using three kinds of systems: UV-C directly photodegradation system, UV/H2O2 and UV/S2O82− system. Under experimental conditions, the degradation rate of 4-t-BP was in the order: UV/S2O82− > UV/H2O2 > UV-C. The reaction kinetics of UV/S2O82− system were thoroughly investigated. The increase of S2O82− concentration enhanced the 4-t-BP degradation rate, which was inhibited when the concentration of S2O82− exceeded 4.0 mM. The highest efficacy in 4-t-BP degradation was obtained at pH 6.5. The oxidation rate of 4-t-BP could be accelerated by increasing the reaction temperature and irradiation intensity. The highest rate constant (kobs = 8.4 × 10−2 min−1) was acquired when the reaction temperature was 45°C. The irradiation intensity was measured by irradiation distance, and the optimum irradiation distance was 10 cm. Moreover, the preliminary mechanism of 4-t-BP degradation was studied. The bond scission of the 4-t-BP molecule occurred by the oxidation of SO4•−, which dimerized and formed two main primary products. Under the conditions of room temperature (25°C±1°C) and low concentration of K2S2O8 (0.5 mM), 35.4% of total organic carbon (TOC) was removed after 8.5-h irradiation. The results showed that UV/S2O82− system was effective for the degradation of 4-t-BP.

Different reaction mechanisms of diphenylether and 4-bromodiphenylether with nitrous acid in the 355 nm laser flash photolysis of mixed aqueous solution.

The microscopic reaction mechanisms of diphenylether (DPE) and 4-bromodiphenylether (4-BrDPE) with nitrous acid (HNO(2)) in the absence of O(2) have been explored by the 355nm laser flash photolysis. It was proposed that OH radical, from the photolysis of HNO(2), added to DPE forms the C(12)H(10)O-OH adduct while added to 4-BrDPE forms the 4-BrDPE-OH and 4-BrOH-DPE adducts. The first-order decay rate constants of the C(12)H(10)O-OH adduct, 4-BrDPE-OH adduct and 4-BrOH-DPE adduct were measured to be (1.86+/-0.14)x10(5)s(-1), (2.19+/-0.04)x10(5)s(-1) and (1.56+/-0.03)x10(5)s(-1), respectively. The final photolysis products of DPE and HNO(2) identified by GC/MS analysis were phenol, o-hydroxydiphenylether, p-hydroxydiphenylether and p-nitrodiphenylether, while the final photolysis product of 4-BrDPE and HNO(2) identified by LC/MS analysis was mainly the dimer.